QD enhanced LCD TVs

[Anonymous]

http://en.wikipedia.org/wiki/Quantum_dot_display

Seems a new trend of future Flat TV. Any implications on calibration?

Topic

[Anonymous]

YES — MAYBE. There is a phenomenon that becomes increasingly likely to happen as the bandwidth of the light source decreases. Projection lamps, phosphors, CCFLs, and “regular” LEDs including “regular” OLEDs all produce relatively wide-bandwidth light. Blue light is made up of a wide range of frequencies, as are green and red. In many cases (probably most cases), blue and green wavelengths overlap each other and green and red frequencies also overlap each other.

A laser light source would be the ultimate “opposite” of a conventional light source… there is ONE frequency of blue light, ONE frequency of Green light and ONE frequency of Red light. All colors are derived from combinations of these single frequencies. Cyan light will be comprised of 2 frequencies as would yellow and magenta light. All other colors would be composed of 3 frequencies.

Quantum Dot technology is a reduced-bandwidth light source. How much reduced the bandwidth is varies quite a bit (so far), but suffice it to say QD displays are much narrower bandwidth (in regards to light source spectrum) than conventional displays, but considerably wider bandwidth than laser light sources.

Why is this an issue? Because of something called metamerism. As the bandwidth gets smaller and smaller, there is more and more variation in what different people see on the screen. The meter may measure a specific shade of yellow as being perfectly accurate, but people may report that the yellow is muted, or too green, or too red, or too dark or too light (along with a perceived color shift). You ask 100 people what color they see and you can get 80 different answers even though they could all be viewing the display at the same time in the same viewing conditions. You cannot calibrate around this issue. It is something that simply exists with no “workaround”. If you produce a PERFECT calibration on a narrow-bandwidth video display, everybody who ever sees it might see something different. That doesn’t mean your calibration is bad, but it is pretty difficult to defend calibration knowing the viewers may disagree about what they see.

For calibrators, if this turns out to be a significant issue, people may decide to never bother with calibration if everybody sees something different AFTER calibration. Everybody sees something different before calibration so there’s (perhaps) no improvement in image accuracy after calibration because everybody will STILL see something different.

This is a PERCEPTUAL issue with how human vision works when presented with “unnatural” (i.e. narrow bandwidth) light sources that don’t exist in nature. Our eyes adapted to “white” light produced by the sun. That’s a very wide bandwidth light source. The more you reduce the bandwidth, the more perceptual errors you get. And these aren’t “predictable” perceptual errors. People don’t all see the same error(s) in a narrow-bandwidth color of yellow, you get a ‘scattershot’ effect when you have people select the reference color of yellow that they see from the narrow-bandwidth source. Like shooting at a target with a shotgun… more “hits” will be towards the center of the pattern, but the pattern itself can have quite a wide spread. So how do you deal with an owner of a QD display (or laser display or some sort) who sees a less accurate (to them) video display after calibration versus before calibration? You can’t see what the customer sees and your meter cannot be “corrected” to see what the owner sees either. All a calibrator can do is make the video display accurate… but if the owner sees less accurate images when the display is accurate, how has a calibrator helped anything? There is nothing the owner can do to change what they see. As calibrators, we may question our work because WE may not see accurate images when our meter says they are accurate. This is not an optical illusion, it is something real that’s part of the human vision system.

I haven’t seen “anybody” in the calibration “industry” weigh-in on this issue yet. Nor have I seen anything that confirms metamerism is an issue with QD or laser displays. So this is something more than speculation but less than accepted reality for our video calibration efforts. There is a POTENTIAL big problem here but I haven’t seen anything that confirms it yet.

[Anonymous]

Thanks for your informative reply!

How about HDR calibration?

[Anonymous]

@Desmond Chow 4355 wrote:

Thanks for your informative reply!

How about HDR calibration?

Calibration relies on reference standards as a target to work towards. All calibration issues start with the fundamentals. There is no HDR standard yet. Everything at this point is speculation and proposals.

[Anonymous]

Also, the only time HDR will be “right” is when viewing HDR content. There is no consumer (or cinema as far as I know) HDR content now. So purchasing an HDR-capable display and turning HDR on for viewing SD or HD content is going to be as “wrong” as using Dynamic mode or any of the other settings video displays have that marketing departments demand, but that do nothing but make images more inaccurate and unnatural. Ditto for wide color gamut… without wide color gamut sources, applying a wide color gamut feature to SD or HD content will just make images look less accurate because the TV can only GUESS at what color was intended in the original content.
Maybe someone from TXH can comment on HDR for cinema… today’s illumination technology and cinema screen sizes make it difficult to get more than 16 fL white on a cinema screen. How the heck will cinema projectors get to the point they can produce 160 or more fL in order to be able to support HDR? Are we getting to a point where home video is going to outperform cinema in this regard? Or will cinema get rid of projectors and switch to giant-flat-panel displays in order to move into “HDR” imaging? It is difficult to imagine seeing 160 fL white on a screen the size of a cinema screen! The theater will be flooded with light.

[Anonymous]

Doug,

Here’s a link to a recent Scott Wilkinson article about HDR Cinema features: http://www.avsforum.com/five-new-movies-in-dolby-vision-hdr/ . There are links part way into the article to Scott’s previous reports on specific movies he’s experienced. Only laser projection has the light output available. There are precious few laser projector equipped venues in America. You are fortunate to live in California, where there are maybe two, possibly even in SF Area. You can check the Dolby site to see where Dolby Vision HDR features can be seen.

[Author]

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